There is a great demand for portable display systems that can project the output of a portable computer to an audience in a small conference room. The ideal portable display system is small, lightweight, inexpensive, quiet, and able to project a very bright image onto a relatively large screen. Designing a successful projector requires tradeoffs between several of these characteristics.
Digital micromirror devices (DMD™) are an ideal spatial light modulator (SLM) for portable display projectors. The digital nature of the DMD provides excellent immunity to electrical noise in the projector circuitry. The extremely fast response time of a DMD enables DMD-based display systems to use pulse width modulation techniques to create intermediate intensity levels.
Color images can be formed simultaneously by three SLMs, each providing a monochromatic image that is combined with the output from the other SLMs to create a full-color image. Alternatively, color images are created by sequentially producing three single-color images with a single SLM. The three single color images are created using a white light source in combination with a spinning color wheel.
The color wheel typically holds three filters, one for each of the three primary colors. A motor drives the color wheel to temporally divide the beam of white light from the light source into three sequential single-color light beams. The motor driving the color wheel is synchronized with the operation of the SLM so that primary color data is driven to the SLM when the proper color filter is in the light path.
The use of a color wheel eliminates the need for three SLMs. Using only one SLM reduces the cost of a display system and eliminates the complex task of optically aligning three SLMs. The use of a single SLM, however, requires the use of a motor and color wheel as well as circuitry to synchronize the color wheel with the SLM. Furthermore, the use of a color wheel increases the size and power consumption of the projector.
As portable projectors continue to improve, consumers expect the size and power consumption of portable projectors to fall further. These expectations eventually become impossible to meet with a color-wheel based system. What is needed is a system and method for creating a full-color image using a single SLM without a moving filter apparatus such as a color wheel or drum.